A normal ear transmits sounds as shown in FIG. 1 through the outer ear 101 to the tympanic membrane (eardrum) 102, which moves the bones of the middle ear 103, which in turn vibrate the oval window and round window openings of the cochlea 104. The cochlea 104 is a long narrow duct wound spirally about its axis for approximately two and a half turns. The cochlea 104 includes an upper channel known as the scala vestibuli and a lower channel known as the scala tympani, which are connected by the cochlear duct. The scala tympani forms an upright spiraling cone with a center called the modiolar where the spiral ganglion cells of the acoustic nerve 113 reside. In response to received sounds transmitted by the middle ear 103, the fluid filled cochlea 104 functions as a transducer to generate electric pulses that are transmitted to the cochlear nerve 113, and ultimately to the brain. Hearing is impaired when there are problems in the ability to transduce external sounds into meaningful action potentials along the neural substrate of the cochlea 104.
In some cases, hearing impairment can be addressed by a cochlear implant that electrically stimulates auditory nerve tissue with small currents delivered by multiple electrode contacts distributed along an implant electrode. FIG. 1 shows some components of a typical cochlear implant system where an external microphone provides an audio signal input to an external signal processing stage 111 which implements one of various known signal processing schemes. The processed signal is converted by the external signal processing stage 111 into a digital data format, such as a sequence of data frames, for transmission by an external coil 107 into an implant receiver 108. Besides extracting the audio information, the implant receiver 108 may perform additional signal processing such as error correction, pulse formation, etc., and produces a stimulation pattern (based on the extracted audio information) that is sent through connected wires 109 to an implant electrode 110. Typically, the implant electrode 110 includes multiple electrodes on its surface that provide selective stimulation of the cochlea 104.
Insertion and placement and insertion of the implant electrode 110 into the cochlea 104 causes trauma to the cochlear tissue due to the rigidity, friction, and impact of moving the implant electrode 110 through the cochlea 104. For example, insertion of the implant electrode 110 may damage soft tissues, membranes, thin bony shelves, blood vessels, neural elements, etc. In the case of multiple insertions, the damage can accumulate. In addition, removal and replacement of the implant electrode 110 due to device failure or aging is also a serious problem. For example, patients with some residual hearing now receive hybrid implant systems that also include acoustic-mechanical stimulation components, and further hearing loss could occur when the implant electrode 110 is removed or replaced. In addition, there are efforts to use therapeutic drugs to regrow neural tissue around an inserted implant electrode 110 which could suffer catastrophic consequences when the electrode is removed since any new neural tissue growth that might reach the electrode could be disrupted or destroyed.
Thus, designers of the implant electrode 110 work hard to ensure that it is soft and flexible to minimize the insertion trauma. The implant electrode 110 also is constrained to have a uniform external aspect with a smooth outer surface. The impact of electrode insertion in certain regions of the inner ear is also addressed by using a pre-shaped (i.e., pre-curved) implant electrode 110. But the issues associated with cummulative permanent trauma due to multiple explantation and re-implantion of the implant electrode 110 has not been addressed.